/* ============= Reading bar ============= */
.reading-bar {
  position: fixed;
  top: 64px;
  left: 0;
  right: 0;
  height: 3px;
  background: transparent;
  z-index: 49;
}

.reading-bar-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  width: 0;
  transition: width .1s linear;
}

/* ============= Chapter layout ============= */
.chapter-layout {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr) 280px;
  gap: 48px;
  padding: 48px 24px 80px;
  max-width: 1400px;
  margin: 0 auto;
}

@media (max-width: 1100px) {
  .chapter-layout { grid-template-columns: 220px minmax(0, 1fr); }
  .chapter-aside-right { display: none; }
}

@media (max-width: 820px) {
  .chapter-layout { grid-template-columns: 1fr; gap: 24px; padding: 24px 16px 60px; }
  .chapter-aside-left { display: none; }
}

/* Left sidebar: chapter list */
.chapter-aside-left {
  position: sticky;
  top: 96px;
  height: calc(100vh - 120px);
  overflow-y: auto;
  padding-right: 12px;
}

.aside-title {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: .14em;
  color: var(--ink-mute);
  font-weight: 600;
  margin: 0 0 12px;
}

.aside-list {
  list-style: none;
  padding: 0;
  margin: 0 0 28px;
  font-size: 14px;
}

.aside-list li {
  padding: 6px 0;
}

.aside-list a {
  color: var(--ink-soft);
  display: block;
  padding: 4px 8px;
  border-radius: 4px;
  border-left: 2px solid transparent;
  font-size: 13px;
  line-height: 1.5;
}

.aside-list a:hover {
  color: var(--accent);
  background: var(--bg-soft);
}

.aside-list a.current {
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 600;
  background: var(--bg-soft);
}

/* Right sidebar: TOC + ad */
.chapter-aside-right {
  position: sticky;
  top: 96px;
  height: calc(100vh - 120px);
  overflow-y: auto;
}

.toc-on-page {
  margin-bottom: 28px;
}

.toc-on-page ul {
  list-style: none;
  padding: 0;
  margin: 0;
  border-left: 1px solid var(--line);
}

.toc-on-page li a {
  display: block;
  padding: 5px 12px;
  font-size: 13px;
  color: var(--ink-soft);
  border-left: 2px solid transparent;
  margin-left: -1px;
}

.toc-on-page li a:hover { color: var(--accent); }
.toc-on-page li a.active {
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 600;
}

/* ============= Chapter main ============= */
.chapter-main {
  max-width: var(--reading);
}

.chapter-meta {
  display: flex;
  gap: 12px;
  align-items: center;
  font-size: 13px;
  color: var(--ink-mute);
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.chapter-meta .pill {
  background: var(--bg-soft);
  padding: 4px 12px;
  border-radius: 99px;
  font-weight: 500;
  color: var(--ink-soft);
}

.chapter-title {
  font-family: var(--font-display);
  font-size: clamp(32px, 4.5vw, 52px);
  line-height: 1.1;
  letter-spacing: -.02em;
  margin: 0 0 12px;
  font-weight: 700;
  color: var(--ink);
}

.chapter-subtitle {
  font-size: 18px;
  color: var(--ink-soft);
  font-style: italic;
  margin: 0 0 16px;
  font-family: var(--font-display);
}

.chapter-actions {
  display: flex;
  gap: 8px;
  margin: 24px 0 32px;
  padding: 16px 0;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  flex-wrap: wrap;
  width: 100%;
}

.action-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 6px 12px;
  font-size: 13px;
  color: var(--ink-soft);
  cursor: pointer;
}

.action-btn:hover { background: var(--bg-soft); color: var(--ink); }
.action-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }
[data-theme="dark"] .action-btn.active { color: #04201d; }

/* ============= Chapter typography ============= */
.chapter-content {
  font-size: 17px;
  line-height: 1.85;
  color: var(--ink);
  overflow-wrap: break-word;
  word-wrap: break-word;
}

.chapter-content > *:first-child { margin-top: 0; }

.chapter-content h2 {
  font-family: var(--font-display);
  font-size: 30px;
  letter-spacing: -.015em;
  margin: 56px 0 16px;
  padding-top: 16px;
  border-top: 1px solid var(--line);
  font-weight: 700;
}

.chapter-content h3 {
  font-family: var(--font-display);
  font-size: 24px;
  margin: 36px 0 12px;
  font-weight: 600;
}

.chapter-content h4 {
  font-size: 19px;
  margin: 24px 0 8px;
  font-weight: 700;
  color: var(--ink);
}

.chapter-content p {
  margin: 0 0 18px;
}

.chapter-content p:has(+ ul), .chapter-content p:has(+ ol) {
  margin-bottom: 8px;
}

.chapter-content ul, .chapter-content ol {
  margin: 0 0 22px;
  padding-left: 26px;
}

.chapter-content li {
  margin: 8px 0;
}

.chapter-content strong {
  color: var(--ink);
  font-weight: 700;
}

.chapter-content em {
  font-family: var(--font-display);
  font-style: italic;
  color: var(--accent);
}

.chapter-content blockquote {
  margin: 24px 0;
  padding: 16px 24px;
  background: var(--bg-soft);
  border-left: 4px solid var(--accent);
  border-radius: 0 8px 8px 0;
  font-style: italic;
  color: var(--ink-soft);
}

.chapter-content a {
  color: var(--accent);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

/* Definition list / glossary */
.glossary {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 22px;
  margin: 28px 0;
}

.glossary dt {
  font-weight: 700;
  color: var(--accent);
  margin-top: 12px;
  font-family: var(--font-mono);
  font-size: 15px;
}

.glossary dt:first-child { margin-top: 0; }

.glossary dd {
  margin: 4px 0 0 0;
  color: var(--ink-soft);
  font-size: 15px;
}

/* Architecture diagram blocks */
.arch-diagram {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 24px;
  margin: 24px 0;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--ink-soft);
  line-height: 1.5;
  white-space: pre-wrap;
  word-break: break-all;
  overflow-x: hidden;
}

/* Comparison cards */
.compare-cards {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 24px 0;
}

@media (max-width: 600px) {
  .compare-cards { grid-template-columns: 1fr; }
}

.compare-card {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
}

.compare-card h4 {
  font-family: var(--font-display);
  font-size: 20px;
  margin: 0 0 12px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--accent);
}

.compare-card ul {
  margin: 0;
  padding-left: 20px;
  font-size: 14px;
}

/* Chapter footer */
.chapter-footer {
  margin-top: 64px;
  padding-top: 32px;
  border-top: 1px solid var(--line);
}

.summary-box {
  background: var(--accent-soft);
  border-radius: var(--radius-lg);
  padding: 28px;
  margin: 32px 0;
}

[data-theme="dark"] .summary-box {
  background: color-mix(in srgb, var(--accent) 15%, var(--bg-elev));
}

.summary-box h3 {
  font-family: var(--font-display);
  font-size: 22px;
  margin: 0 0 12px;
  color: var(--accent-ink);
}

[data-theme="dark"] .summary-box h3 { color: var(--accent); }

.summary-box ul {
  margin: 0;
  padding-left: 22px;
}

.summary-box li {
  color: var(--accent-ink);
  margin: 6px 0;
}

[data-theme="dark"] .summary-box li { color: var(--ink); }

.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 48px;
  flex-wrap: wrap;
}

.nav-link {
  flex: 1;
  min-width: 240px;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 20px;
  color: var(--ink);
  display: block;
  transition: all .15s ease;
}

.nav-link:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
  color: var(--ink);
}

@media (max-width: 600px) {
  .nav-link { min-width: 100%; }
  .chapter-actions { gap: 8px; justify-content: stretch; }
  .chapter-actions .action-btn { font-size: 13px; padding: 10px 12px; flex: 1 1 140px; justify-content: center; white-space: normal; text-align: center; }
}

@media (max-width: 440px) {
  .chapter-actions .action-btn { flex: 1 1 100%; }
}

.nav-link .nav-label {
  font-size: 12px;
  color: var(--ink-mute);
  text-transform: uppercase;
  letter-spacing: .1em;
}

.nav-link .nav-title {
  font-family: var(--font-display);
  font-size: 18px;
  margin-top: 4px;
  font-weight: 600;
}

.nav-link.next { text-align: right; }

/* ============= Buttons ============= */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border-radius: 8px;
  font-size: 15px;
  font-family: var(--font-bn);
  font-weight: 600;
  cursor: pointer;
  border: 1.5px solid transparent;
  transition: all .15s ease;
  white-space: normal;
}

.btn-primary {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.btn-primary:hover {
  opacity: .88;
  transform: translateY(-1px);
}

[data-theme="dark"] .btn-primary { color: #04201d; }

.btn-ghost {
  background: transparent;
  color: var(--ink-soft);
  border-color: var(--line);
}

.btn-ghost:hover:not(:disabled) {
  background: var(--bg-soft);
  color: var(--ink);
  border-color: var(--ink-mute);
}

.btn:disabled {
  opacity: .38;
  cursor: not-allowed;
}

/* ============= Quiz ============= */
.quiz-section {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: 32px;
  margin: 48px 0;
}

.quiz-header {
  text-align: center;
  margin-bottom: 24px;
}

.quiz-header h2 {
  font-family: var(--font-display);
  font-size: 28px;
  margin: 0 0 8px;
  border: none;
  padding: 0;
}

.quiz-header p {
  color: var(--ink-soft);
  margin: 0;
}

.quiz-question {
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 16px;
  display: none;
}

.quiz-question.active { display: block; }

.q-num {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--accent);
  font-weight: 600;
  margin-bottom: 8px;
}

.q-text {
  font-size: 17px;
  font-weight: 500;
  margin: 0 0 20px;
  line-height: 1.6;
}

.q-options {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.q-option {
  background: var(--bg-elev);
  border: 1.5px solid var(--line);
  border-radius: 8px;
  padding: 12px 16px;
  cursor: pointer;
  font-size: 15px;
  display: flex;
  align-items: center;
  gap: 12px;
  transition: all .15s ease;
}

.q-option:hover {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 5%, var(--bg-elev));
}

.q-option.selected {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 12%, var(--bg-elev));
}

.q-option.correct {
  border-color: var(--success);
  background: color-mix(in srgb, var(--success) 12%, var(--bg-elev));
}

.q-option.wrong {
  border-color: var(--danger);
  background: color-mix(in srgb, var(--danger) 12%, var(--bg-elev));
}

.q-letter {
  display: inline-grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--bg-soft);
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 13px;
  flex-shrink: 0;
}

.q-explain {
  display: none;
  margin-top: 16px;
  padding: 14px 18px;
  background: var(--accent-soft);
  border-left: 3px solid var(--accent);
  border-radius: 0 8px 8px 0;
  font-size: 14px;
  color: var(--accent-ink);
}

[data-theme="dark"] .q-explain { color: var(--ink); background: color-mix(in srgb, var(--accent) 15%, var(--bg-elev)); }

.q-explain.visible { display: block; }

.quiz-controls {
  display: flex !important;
  justify-content: space-between;
  align-items: center;
  margin-top: 32px;
  gap: 12px;
  flex-wrap: wrap;
  padding-top: 24px;
  border-top: 1px solid var(--line);
  visibility: visible !important;
  opacity: 1 !important;
}

@media (max-width: 500px) {
  .quiz-controls { flex-direction: column; align-items: stretch; }
  .quiz-progress { text-align: center; order: -1; margin-bottom: 8px; }
}

.quiz-progress {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--ink-soft);
  font-weight: 500;
}

.quiz-result {
  text-align: center;
  padding: 48px 24px;
  display: none;
}

.quiz-result.shown { display: block; }

.result-score {
  font-family: var(--font-display);
  font-size: 64px;
  font-weight: 700;
  color: var(--accent);
  line-height: 1;
}

.result-label {
  font-size: 18px;
  color: var(--ink-soft);
  margin: 8px 0 16px;
}

.result-message {
  font-size: 17px;
  margin: 0 0 24px;
  font-family: var(--font-display);
  font-style: italic;
}

/* Modal (profile prompt) */
.sdb-modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.5);
  display: grid;
  place-items: center;
  z-index: 100;
  padding: 16px;
}

.sdb-modal {
  background: var(--bg-elev);
  border-radius: var(--radius-lg);
  padding: 32px;
  max-width: 440px;
  width: 100%;
  box-shadow: var(--shadow-lg);
}

.sdb-modal h2 {
  font-family: var(--font-display);
  margin: 0 0 12px;
  font-size: 28px;
}

.sdb-modal p {
  color: var(--ink-soft);
  margin: 0 0 20px;
}

.sdb-modal input {
  width: 100%;
  padding: 12px 16px;
  border: 2px solid var(--line);
  border-radius: 8px;
  font-size: 16px;
  font-family: var(--font-bn);
  background: var(--bg);
  color: var(--ink);
  margin-bottom: 16px;
}

.sdb-modal input:focus {
  outline: none;
  border-color: var(--accent);
}

.modal-actions {
  display: flex;
  gap: 12px;
  justify-content: flex-end;
}